1. Field of the Invention
This invention generally relates to starters, and more particularly to an improvement of a return spring in a starter.
2. Background of the Invention
FIG. 1 shows one example of a conventional starter which has been disclosed, for instance, in Japanese Utility Model application (OPI) NO. 107957/1981 (the term "OPI" as used herein meaning "an unexamined published application"). In FIG. 1 a current supplying terminal M for supplies electric current to a starter 4a. The starter 4a includes a field coil 5 and an armature 6 with an output shaft 8 of the armature 6. The output shaft 8 has helical splines 8a formed on its cylindrical outer wall. A thrust spline member (boss) 9 is slidably mounted on the helical splines 8a and A pinion 10. the pinion 10 is cam-engaged with the trust spline member 9, thus forming an over-running clutch. The pinion 10 slides on the output shaft 8 to engage with a ring gear 14 of the engine to transmit the torque of the armature 6 to the engine thereby to start the engine.
Further in FIG. 1, a stopper 12 is secured to the output shaft 8 with a ring 3. A return spring 11 is mounted on the output shaft 8 in such a manner that it is located between the stopper 12 and the pinion 10. Normally the pinion 10 is biased by the return spring 11 to the left in FIG. 1, so as to be set apart from the ring gear 14.
FIG. 2 shows a general electrical circuit for a starter of this type. When a key switch 2 is turned on, current is caused to flow from a battery 1 to the switch coil 3d of an electromagnetic switch 3. As a result, the plunger 3e of the switch 3 is attracted by the switch coil 3d to bring a movable contact 3c into contact with stationary contacts 3a and 3b, i.e., to close the normally-open contact means comprising the stationary contacts 3a and 3b and the movable contact 3c. As a result, the voltage of the battery 1 is applied to the terminal M of the starter 4a shown in FIG. 1, to allow current to flow in the field coil 5 and the armature 6, so that the armature is rotated. Therefore, owing to the angle of inclination of the helical splines 8a of the output shaft 8 and the inertia of the thrust spline member 9 and the pinion 10, the pinion 10 is moved against the elastic force of the return spring 11 to the right in FIG. 1, to engage with the ring gear 14 of the engine to thereby start the engine.
When the key switch 2 is turned off, the movable contact 3c is disengaged from the stationary contacts 3a and 3b by a contact spring (not shown) as shown in FIG. 2, thereby to interrupt the energization of the starter 4a, while the pinion 10 is disengaged from the ring gear 14 by the elastic force of the return spring 11.
One example of a starter is disclosed in Japanese Utility Model Application Publication No. 55-41563. In this starter, a brake is disposed adjacent a slider member which is in enagreement with a helical spline. Further, a drive means is provided to actuate the brake.
Another example of a starter is disclosed in Japanese Utility Model Application Publication No. 57-36763. According to this starter, a movable shaft is provided which is actuated by an electromagnetic force of a solenoid which functions as a stop to hold the engagement between a pinion and a ring gear. Further, a contact mechanism is provided which the utilizes electromagnetic force of the solenoid.
The conventional starter is constructed as described above. Therefore, dust or water is liable to enter the starter to deposit at or around the return spring to make the sliding operation of the return spring unsatisfactory or to corrode and break it. In order to overcome these difficulties, a variety of methods have been proposed, such as for instance, a method of providing a protective cover. However, none of the methods are sufficient. Furthermore, the starter suffers from a problem that, before the engine is started completely, the pinion returns, so that the engine cannot be started. In addition, the conventional starter has the following disadvantage. Since, in order to quickly eject the pinion, it is essential to completely stop the armature, it is necessary to provide a brake device for the armature or to wait until the armature stops.